Pressure controlled cutter bit retainer with precision adjustable cutter bit

ABSTRACT

A pressure controlled cutter bit or drill bit retainer in the form of a revolving drill head with hydraulic precision adjustment of the drill bit arranged at a central extension, which is displaceable from its original position by small amounts around a pivot axis by a pressure motor, wherein this displacement occurs without any parts mechanically rubbing against each other and the dimensioning of the pressure motor and extension defining the transmission ratio conditions are selected in such a way that the travel of the drill bit guided along a curved path is greater than the travel of the pressure motor output produced by volume change, and wherein the overall volume of the pressure motor is selected to be slightly greater than the volume required for moving the pressure motor output.

BACKGROUND OF THE INVENTION

The invention is directed to a pressure controlled cutter bit or drillbit retainer with a clampable cutter bit or drill bit, especially ahydraulically precision adjustable rotating drill head, with a pressuremotor, comprising a base and an output sealed and resiliently mobilewith respect to the base. Additionally, a mobile pressure seal, apressure fluid chamber and a fluid supply are present, as well as anapparatus that converts motion of an output part into movement of thecutter bit on a curved path which extends approximately perpendicular tothe axis of rotation.

The invention serves for solving the requirement occurring increasinglyin modern manufacturing technology of fabricating internal cylinderbarrel surfaces or areas as rapidly and accurately to size as possible,whole surface contour as a function of the travel of the drill bitparallel to the axis of rotation and as a function of the angle ofrotation of the drill bit relative to the workpiece, deviates at most by500 to 1,000 μ from an exactly cylindrical barrel or jacket surface witha tolerance in the 1 μ-range±50%. Such untrue or out-of-center holeswhose surface thus deviates polarity-wise or axially from an axiallyparallel straight line or from an axially concentric circle can only beimperfectly produced or manufactured by the drill bit retainers of thetype being discussed here and known hitherto, which are also designatedas drill heads. Assuming that the control pressure source provides therequired control pressure at the right time and in the requiredmagnitude, the mechanical actuation means of these drill heads mustsimultaneously have the following properties:

1. The drill or cutter bit must respond sufficiently accurately andwithout hysteresis effect to the control pressure; and

2. The natural frequency of the drill head must lie distinctly above thecontrol pressure frequency. If these frequencies differ only by a smallamount, then resonance effects occur which render the drill headunusable for utilization above this frequency range.

The drill heads in the state of the art fulfill either one or the otherassumption. However, they do not fulfill both simultaneously.

Thus, in the drill head in U.S. Pat. No. 3,007,356, the driven end ofthe shaft transmits its excursion to the drill bit by means of partsrubbing against each other. Due to this friction, such a drill headcannot respond to small pressure changes whose effect does not exceedthe frictional forces and also in case of larger forces, the drill bitposition is not reproducibly linked with the control pressure, which hasthe effect that the same control pressure, depending on whether it isrising or falling, causes different drill bit positions or attitudes.

The drill heads in the teaching of DE 20 34 601-A2 and DE 22 58 553-A1have indeed no friction and therefore produce workpieces true todimensioning. However, their natural frequency is low because thereduced mass inertia moment referred to the drilling bit of all theparts moving relative to the base and, therefore, participating in anoscillation or vibration is large.

All drill heads in the state of the art have the additional disadvantageof comprising a large fluid chamber. With a large fluid chamber, becauseof the compressibility of the pressure fluid, a relatively largequantity of fluid must flow into or out of the fluid chamber through afluid supply line offering a resistance for building up a specificpressure in the fluid chamber. Thus, a certain time is required untilthe pressure in the fluid chamber equals the control pressure. In thecase of rapidly changing control pressure, the chamber pressuretherefore deviates, as far as pressure amplitude and phase areconcerned, from the control pressure upstream of the fluid supply andtherefore positioning errors of the drill or boring bit occur.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to improve theknown pressure controlled drill bit retainers mentioned above and torefine them so that the changes of position of the drill bit can followwith the smallest delay possible a predetermined volume change in theassigned fluid chamber and with this force changes of the output canfollow in a proportional manner and with the least delay possible, sothat especially internal out-of-round cylinder barrel surfaces withdeviations from the exact cylinder jacket shape of 500 to 1,000 μ can befabricated better and more accurately than hitherto with a tolerance inthe 1 μ range±50%.

Pursuant to this object, and others which will become apparenthereafter, one aspect of the present invention resides in providing arigid connection between the pressure motor output and the cutter bit,which rigid connection has no parts which mechanically rub against eachother. Additionally, the output part has a travel which is smaller thanthe travel of the cutter bit.

Because of the design shape of the drill bit retainer in the invention,the reduced mass inertia moment of all parts moving with respect to thebase and therefore participating in a vibration or oscillation referredto the drill bit becomes smaller than that of the known pressurecontrolled drill heads, where drill bit and pressure motor output coverthe same travel in the course of their displacement: All this isreferred to the same dimensions and masses of the drilling rodconnecting the drill bit with the pressure motor output in the state ofthe art and in the invention. This entails that, thanks to theinvention, the natural frequency of the drill head is higher than thatof the known pressure controlled drill heads with otherwise equal springstiffness or spring rate of the drill bit in the direction of itsadvancing travel. The drill bit of the drill head retainer in theinvention thus responds considerably faster dimensionally accurately tothe pressure changes of the fluid influencing it in its adjustmentposition.

A further advantage is that the spring stiffness or rate which can bemeasured at the drill bit and which is referred to its travel isdetermined essentially only by the inherent stiffness of the pressuremotor. Finally, the measure of the design version of the drill bitretainer and of its drive means in the invention in a manner that theentire volume of the pressure means in the pressure motor is onlyslightly larger than the volume required for movement of the pressuremotor output is especially advantageous and not only in drill bitretainers in the invention.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view partially in section showing a drill bit retainerpursuant to the invention depicted as a revolving drill head;

FIG. 2 is a section along the line II--II of FIG. 1, on a smaller scale;

FIG. 3 is a section through line III--III of FIG. 1, on a smaller scale;

FIG. 4 is a side view shown partially in section of a second embodimentof a drill bit retainer of the invention, designed as a revolving drillhead; and

FIG. 5 is a plan view shown partially in section of the drill bitretainer of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the invention is shown in FIG. 1, where two parts10 and 11 form a hydraulic drill head Bkl. The part 10 is a flat turnedpart with a circular cross-section which is subdivided into two segmentsby an eccentric recess 12 in the region of the sectional line II--II.One of the two segments is a thin plate 13 and the other segment forms athick plate 14, which segments remain connected with each other by around, eccentrically located segment 15. This relatively thin plate 13formed by the recess or turned-down region in the upper portion of part10 has approximately the shape of a closed "sickle" or "crescent"--seeFIG. 3--and is resilient with respect to the segment forming the lowerplate 14 and serves simultaneously as a mobile pressure seal for thepressure motor DM₁ which remains to be described. The wide part of thesickle lies on the right-hand side and the narrow part on the left-handside, with reference to FIG. 2. On the narrow part, the plate 13comprises, on a side facing away from the plate, an extension 16 shapedlike a cylindrical jacket, which is arranged coaxially to the axis ofsymmetry 17 which is simultaneously the axis of rotation of the drillhead and which extension 16 forms part of the pressure motor DM₁. Thepart 10 thus forms the rigid base of the pressure motor, which stillremains to be explained.

The part 11 carries the drill rod 21 which includes the drill bit 20,and comprises an also centrally arranged piston shaped extension 23 at aside facing away from the drill rod 20, which extension 23 engages intothe cylinder jacket shaped extension 16. The part 11 is fixedlyconnected in a leak proof manner with the part 10 by means of screws 25and a seal in the form of a toroidal sealing ring 26 between facingcylinder jacket surfaces of the extensions 16 and 23. A fluid space orfluid chamber 27 is formed between the piston shaped extension 23 andthe cylinder jacket shaped extension 16. The height of this chamber 27as determined by the differing heights of extensions 16 and 23 isselected to be as small as possible due to the disadvantageous effect ofcompressibility of the fluid. The extensions 16 and 23 are part of thementioned pressure motor DM₁, wherein the thin, elastic plate 13 of thepart 10 is rigidly connected by screws 25 with the part 11 forming theoutput of the pressure motor.

Furthermore, the part 10 has holes 28 at the proximity of the outer edgeand a centering flange 29 for attachment of the drill head at thedrilling tool spindle (not shown here). The part 10 further comprises acentral pressure means--or fluid supply line 30--which discharges intothe flat disc-shaped fluid chamber 27.

Such a pressure motor thus comprises a base rigidly connected with theaxis of rotation. The output portion moves with respect to the base whenthe pressure of the pressure fluid changes. Base and output partsembrace the fluid chamber, which has a fluid supply offering resistanceto flow. So that the fluid chamber remains tightly sealed in spite ofthe motion of the output part, a mobile seal is provided. The outputtravel is the travel or path of the center of gravity of the output partwith respect to the base caused by the change in pressure.

The control pressure source required for generation of the necessarycontrol pressure is neither shown nor described since it is known assuch and does not form part of the invention. The functional mode of thedescribed arrangement is as follows:

If the pressure of the pressure means, in this case a fluid madeavailable by the pressure source not shown here, is increased, then thefluid entering the space 27 will attempt to occupy a larger volume.Herein the right-hand part of the resilient plate 13, referring to FIG.1, is more significantly deformed than the left-hand part because of themoment of resistance weakened by the recess 12. The part 11 thus pivotsapproximately counter clockwise around a pivot axis near the plane ofthe pressure motor, forming itself eccentrically with reference to theaxis of symmetry 17. If the pressure of the fluid reverts to theoriginal pressure, then the plate 13 springs back to its originalposition and the drill rod also assumes its original position. Thestiffness of this arrangement is defined by the dimensioning of itscomponents, especially by the dimensioning of the resilient plate 13.

It is evident herein that the part 11 acting as the pressure motoroutput covers a smaller travel than the cutter bit or drill bit 21moving along a curved path, and that the fluid volume of the entirearrangement is small and therefore the natural frequency of the drillhead described is higher than in an arrangement with a drill rod, whichmoves parallel to the axis of symmetry 17 (DE 20 34 601 A2) because of aparallel spring joint during the drill bit advance.

Naturally, the drill rod can also be connected with the plate by meansof a tool bit change system of known construction instead of thedescribed rigid connection of the drill rod with the plate 11.

Another embodiment of the drill head of the invention designated Bk2 isshown in FIGS. 4 and 5. Here also the part forming the base plate isdesignated by 10 and the part carrying the drill rod 21 is designated by11. Here also the drill head is fastened by means of the part 10 to thedrilling spindle of a drilling machine tool, not shown here. Here alsothe pressure motor designated DM₂ comprises an extension 16 shaped as acylinder jacket forming the base 10 and a piston shaped extension 23,wherein both extensions corresponding with each other are located on theparts 10 and 11 outside of the line of symmetry 17. The extensions 16and 23 are fixed, connected detachably or non-detachably, with theassociated plates sealed against each other by an elastomeric sealstressed by squeezing and they enclose the fluid space 27 betweenthemselves.

The plate 10 forming the base is connected with the plate 11 forming theoutput of the pressure motor and carrying here the piston shapedextension 23 without play preferably by means of spring members 36 and37. The drilling rod 21 carrying the drill bit 20 is fixedly connectedso as to be able to be replaced rigidly or by means of a tool bitreplacement system. The pressure means or fluid is directed by an axialbore 31 extending in angled fashion to the fluid space 27 of thepressure motor.

If the pressure of the supplied pressure means rises, then the part 11pivots counterclockwise around an axis extending approximately throughthe centers of the spring members 36 and 37 in the plane of the pressuremotor.

The stiffness of the arrangement described in FIGS. 4 and 5 isessentially defined by the bending strength of the spring members 36 and37 which are configured so as to be replaceable. This way the jointformed by the two spiral springs can be changed as far as its rigidityor stiffness is concerned. It can, for instance, be attained thereinthat with a predetermined maximum control pressure of 200 bar, the drillbit covers small travels if the drill head has a high stiffness and ahigh natural frequency and covers larger travels with a lower stiffness.This is important when adapting the drill head to the differentmaterials which have to be machined by the cutter bit or serves forincreasing the natural or inherent frequency if one can work withsmaller maximum adjustment or actuation travels.

Naturally, a Bourdon tube or a metal capsule can be used as a pressuremotor. Also, other known pressure motor designs, for instance in theform of a supported rubber diaphragm, are usable for this purpose.

While the invention has been illustrated and described as embodied in apressure controlled cutter bit retainer with a precision adjustablecutter bit, 76 it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by letters patent isset forth in the appended claims.
 1. A boring apparatus, comprising:arotating hydraulic pressure controlled cutter bit retainer with aprecision adjustable boring bar bearing a cutter bit; a base; and anintegrated pressure motor having a pressure fluid chamber and an outputpart sealed and resiliently mobile with respect to said base, thepressure motor output part and the boring bar being a rigid unit withoutany parts which mechanically rub upon each other, so that displacementof the output part caused by a volume of pressure fluid is smaller thandisplacement of the cutter bit upon a curved path extendingapproximately perpendicularly to the axis of rotation of the cutter bit,the output part having a pivot axis tiltable with respect to said baseand located externally of the axis of symmetry of the boring bar, theoutput port being a round plate tiltable with respect to said base, andfurther comprising an elastomeric seal for sealing said round plate in amobile manner against said base, said elastomeric seal being stressed bysqueezing, and said round plate being connected with said base in aresilient manner by two replaceable elastic rods.
 2. A boring apparatusaccording to claim 1, wherein the base (10) is a base plate with whichthe two elastic rods (36, 17), arranged externally of the axis ofsymmetry (17) of the boring bar, are connected.
 3. A boring apparatusaccording to claim 1, wherein the elastic rods are elastic springmembers.
 4. A boring apparatus according to claim 3, wherein the elasticspring members (36, 37) define a spring stiffness and excursion of thepressure motor output part and are replaceable by different springmembers with another spring stiffness which are replaceable withoutresulting in any play.